Destination Dunes: transdisciplinary collaboration
The City of Cape Town’s New Water Programme involves the development and operation of the Cape Flats Aquifer Management Scheme which includes abstraction and managed aquifer recharge (MAR) to augment the bulk potable supply of the City Metropole to avoid another 2017 Day Zero scenario. The Managed Aquifer Recharge Scheme will ultimately serve to improve the water quality of the Cape Flats Aquifer, a task that contributes to the sixth Sustainable Development Goal (SDG; Clean water and Sanitation). This will be done through recharging the aquifer with high quality treated effluent which in the long run intends to improve water quality within the aquifer. Groundwater is then abstracted, treated at water treatment works before being used for potable supply. The scheme also aims to prevent, locate and rehabilitate any contamination of the aquifer through Groundwater Protection Zones. A mandate that specifically speaks to SDG 6.6, that aims to protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes.
With development comes environmental protection which has called for transdisciplinary collaboration between engineers, scientists, policy makers and the general public to protect the Cape Flats wetlands and assess their reliance on groundwater within the Cape Flats Aquifer (CFA) which is targeted by the scheme. An initiative that strives towards reaching SDG 15.1, namely the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services.
In the Cape Flats region this will be achieved through communication between paralleling efforts of groundwater abstraction and recharge operations, groundwater level monitoring and Umvoto’s wetland monitoring programme. During our monitoring work, Umvoto had the opportunity to assess the wetland’s connection to the underlying groundwater, and saw many journeys through the sands of time to determine the presence and extent of the Cape Flats wetlands.
A forgotten aquatic network
The Cape Flats Wetlands, more formally known as Cape Lowland Wetlands were once a wide expanse of interconnecting wetland-river transitional waterbodies that flowed as concentrated channels in winter and dried to oozing diffuse trickles in summer.
This network of aquatic wetlands has been impacted over the last few decades primarily through alien vegetation, fragmentation and habitat loss due to urban and agricultural development that have seen catchment waters bypassed to sea via canalized rivers and stormwater infrastructure. The remnant wetlands we see today are thus mostly isolated components of a once larger wetland network system and are in need of conservation and protection.
Deciphering between moisture and mirage
Searching for wetlands on the Cape Flats nowadays is like searching for water in the desert, you need to avoid delirium if you’re hoping to spot an actual wetland. That’s because to the untrained eye there is often no discreet boundary between dryland and wetland areas. In fact, the wet areas are often not wet at all, but at best moist, and just enough to exclude non-wetland vegetation.
The stigma associated with wetlands is that they need to be flooded with water, flocked by flamingos and vegetated with iconic reeds. The Cape Flats wetlands however developed on a dynamically shifting well-drained sandy dune system that through aeolian action has created topographic high areas (dunes) which through the process of rainfall, percolation and inter-flow provide moisture to the topographic low areas, creating wetlands. As such, the majority of Cape Flats wetlands are formally referred to as duneslack wetlands. Augered soil profiles only reveal cool to slightly moist soils essentially devoid of redoximorphic features (soil morphological features that form as a result of alternating periods of soil reduction and oxidation) upon which the rest of the country identify wetlands on.
When these indications are absent, one has to rely on the presence of known wetland plants on the Cape Flats which include low growth shrubs, restios, sedges and grasses such as Passerina paludosa, Imperata cylindrica, Roepera flexuosa, Restio curviramus, Elegia tectorum and Zantedeschia aethiopica to name a few.
The wetlands of the Cape Flats belong to the Sand Fynbos and Dune Strandveld vegetation veld types which are critically endangered due to loss of habitat and very little of the remaining habitat proclaimed for conservation.
The role of insect and mammal pollination and seed dispersal is paramount to the survival of the remaining wetland communities and as such every effort should be made to construct/maintain green belts between wetland clusters to allow the safe commute of animals.
Two butterflies from the family Hesperiidae solely rely on the wetland sword grass, Imperata cylindrica. According to the Kedestes Conservation Project these are on the brink of extinction within the next 5 years unless staunch conservation action is taken. These are the Unique Ranger (Kedestes lenis lenis) and the Barber’s Ranger (Kedestes barberae bunta) butterflies which form part of the Kedestes Conservation Project which carries out a range of habitat restoration and protection work, abundance surveys and a captive rearing and breeding programme.
Indeed for the first time does an opportunity present itself to utilize our in depth understanding of the Cape Flats Aquifer to guide a Managed Aquifer Recharge Scheme to not only maintain the intricate divide between freshwater and terrestrial areas, but redress historic activities that resulted in wetland destruction.